1. Field of the Invention
The present invention relates to electron-optical systems with variable-shaped beams for generating and measuring microstructures, and in particular to such a system which minimizes the number of beam crossover points and significantly shortens the electron beam path.
2. Description of the Prior Art
Electron-optical lithography devices which are utilized to radiate a resist wafer with a fine electron beam probe for generating a structure pattern thereon are increasingly being employed for generating circuit patterns and structures on semiconductor substrates. Because of the increasingly smaller dimensions of such structures and circuits, the edge definition of the electron beam probe which is utilized to generate the patterns and structures must have a correspondingly improved edge definition given a high probe current. A problem in the design and construction of such electron-optical lithography devices is that the energy and direction of the electrons in the electron beam are changed as a result of interaction of the electrons (Boersch effect) which causes a deterioration in the edge definition of the beam given an increasing beam current. Similar problems also apply to electron beam measuring installations, which also require a highly-defined electron probe with a high probe current.
An electron beam lithography device with a variable-shaped beam is described in the article "Recent Advances in Electron-Beam Lithography for the High-Volume Production of VLSI Devices," Pfeiffer, IEEE Trans. on Electron Devices, Vol. ED-26, No. 4, April, 1979, pages 663-674. In this known electron-optical system, a shaped beam which can be matched to the structure to be generated is moved over a target, such as a resist wafer. In view of the Boersch effect, this known electron-optical system has the disadvantage of an electron beam path of a relatively large length of more than one meter, and a relatively large number of beam intersection or crossover points; the system having a total of five such points. The length of the beam path and the number of locations where the electrons come together particularly tightly promote mutual interaction of the electrons which undesireably leads to the Boersch effect. Apart from the Boersch effect, the large number of lenses (five) and their relatively complicated structure contribute to increased cost in manufacturing and operating such a system.